1. Field of the Invention
This invention generally relates to a rotational displacement apparatus for detecting the angular displacement of a rotating member such as a shaft. More specifically, the present invention relates to an apparatus which detects the crank angle of a multiple cylinder type internal combustion engine, in order to select the cylinder, for controlling the ignition timing or the fuel injection of the engine.
2. Description of the Related Art
It is known in the field of internal combustion engines that the angular displacement of the crank shaft should be measured in correspondence with each stroke, to electronically control the ignition timing or the amount of injected fuel per cylinder. Such strokes range from the intake stroke to the exhaust stroke.
There exist various types of conventional devices for detecting the crank angle (CA). For example, Japanese Unexamined Patent Publication No. 61-213714 discloses one such device. The device described in the above publication includes a first sensor for detecting a unit rotational angle of a crank shaft, a second sensor for detecting an upper dead point of a piston, and a third sensor for specifying a cylinder to be ignited. The first sensor comprises a circular disk, or body fixedly, connected to the crank shaft, and an electromagnetic pickup, which is arranged adjacent to the circular disk. The circular disk has a plurality of projections, or gear teeth, which are arranged at equal circular pitches (for example, CA=30.degree.), along the periphery of the disk. Every time the crank shaft rotates by a predetermined angle (30 degrees), the electromagnetic pickup detects one tooth. Therefore, the first sensor transmits a unit angular signal.
The second sensor comprises a projection formed along the periphery of the crank shaft, and an electromagnetic pickup arranged adjacent to the projection. Whenever the crank shaft makes one revolution (CA=360.degree.), the electromagnetic pickup detects the projection. Thus, the second sensor transmits a first reference signal.
Further, the third sensor comprises a projection formed along the periphery of a camshaft of the internal combustion engine and an electromagnetic pickup arranged adjacent to the projection. Whenever the cam shaft makes one revolution (CA =720.degree.), the electromagnetic pickup detects the projection. The third sensor transmits a second reference signal. As the latter transmitted reference signals are fed into a microcomputer of a detecting unit, the computer calculates an appropriate crank angle corresponding to each stroke of the engine. However, the apparatus for detecting the crank angle described above requires three pickups corresponding to each one of the sensors described above, which leads to an increase in the number of parts.
Japanese National Publication No. 61-502557, which corresponds to the international application No. PCT/DE85/00080, discloses an apparatus for detecting a rotational or angular displacement. The apparatus comprises a circular disk or body, that is fixedly connected to the crank shaft, and an electromagnetic pickup arranged adjacent to the circular disk. The circular disk has a plurality of projections or gear teeth which are arranged at equal circular pitches, along the periphery. As one out of the plurality of projections has been removed from the disk, a first gap between two specific adjacent projections, with a gap therebetween, has a different width, compared to that of a second gap between the remaining adjacent projections.
The sensor transmits unit angle signals at every predetermined angular interval, when the projections that are spaced by the second gap, pass over the electromagnetic pickup. The sensor transmits a reference signal which has a different angular interval, when the projections that are spaced by the first gap, pass over the electromagnetic pickup. Therefore, the sensor disclosed in the above-described publication (61-502557) can be applied to the apparatus disclosed in the above publication (Japanese Unexamined Patent Publication No. 61-213714), as the first and second sensors, for detecting the rotational angle of a crank shaft and for detecting the upper dead point of the piston.
However, it requires a maximum crank angle (CA=720.degree.), before the first cylinder is defined, by changing the configuration of the circular disk in the sensor, which is disposed at the crankshaft side, when four cylinders of the internal combustion engine are activated. Therefore, as this crank angle detecting apparatus is combined with a distributorless ignition system (DLI) of an ignition timing apparatus, for use in a gasoline engine, the engine is caused to ignite after the crankshaft rotates more than 720 degrees. The starting of the engine is slightly delayed. Such problem is similarly generated in a fuel injection system, which injects the fuel independently into each cylinder during the engine activation period, or in a fuel injection system which injects fuel into every group, including multiple cylinders.
The present invention aims at overcoming the foregoing disadvantages of the prior art.